Electromagnetic relay



June 29, 1954 R J, E 2,682,586

ELECTROMAGNETIC RELAY Filed May 27, 1952 2 Sheets-Sheet 1 Fuel.

27 INVENTOR.

R.J.Little WO/ZM,

His ATTORNEY June 29, 1954 LlTTLE 2,682,586

ELECTROMAGNETIC RELAY Filed May 27, 1952 2 Sheets-Sheet 2 FIG. 3. 58

IN V EN TOR.

RJLittle WM/ m His ATTORNEY Patented June 29, 1954 UNITED ELECTROMAGNETIC RELAY Robert J. Little, Gates, N. Y., assignor to General Railway Signal Company, Rochester, N. Y.

Application May 27, 1952, Serial No. 290,241

12 Claims. 1

This invention relates to electromagnetic relays, and. more particularly pertains to contact structures of the so-called non-bounce type adapted for controlling relatively large currents and used in such relays.

In railway signalling systems and in other electrical control systems, it is often desirable to intermittently open and close circuits carrying relatively large currents. When the control circuits include incandescent lamps, it is common knowledge that these lamps draw a much heavier current upon their initial energization that when they have become fully illuminated. In such cases, the contacts which control the circuits should be so constructed as to close the circuits in a positive fashion avoiding any socalled bounce or vibration that may occur. This is because any partial opening of the contacts produces an are which in some cases may be sufliciently hot as to burn the contacts. Obviously, such a burning of the contacts if repeated often enough will cause the disintegration of the contacts in a relatively short time.

One cause for contact bounce is due to the back contacts of a relay acting as the shock absorbing means when the armature is released. In other words, the armature generally has considerable mass, which gains considerable momentum when it is released and this momentum, of course, must be dissipated. when the armature reaches its backstop. Most relays provide a positive backstop for the armature and when this backstop is reached, it is obvious that the armature will bounce away from it and return before settling down to its final deenergized position. Any such bounce of the armature will, of course, be transmitted to the movable contacts of the conventional type relay.

Another cause of contact vibration, particucertain amount of vibration transmitted to the relay armature.

In view of the above considerations, it is proposed in accordance with the present invention to so construct the contacts in relation to the armature, that the contacts may be opened and closed by armature operation, but when the contacts are closed they are wholly free from any mechanical connection to the armature. In this way, any vibration of the armature, due either to its impact with its associated stops, or to vibrations induced from external causes, cannot reach the contacts.

Another feature of the present invention resides in the structure wherein the relay armature is biased to a released position by gravity and is additionally biased by a spring so as to reduce its response to external vibrations to a value insufficient to establish direct mechanical connection with the electrical contacts of the present invention.

A further feature of the present invention is to provide contacts of the so-called non-bounce type in which the relative masses and biasing forces are so interrelated that the abrupt closure of the contacts does not result in a bounce or vibration of the contact fingers, but rather causes a positive and. definite closure of the contacts.

A further feature of the invention is that the contact fingers themselves shall be constructed of such size, shape and materials as to have different natural periods of vibration so that each will have a dampening effect on the other.

Other objects, purposes and characteristic features of the present invention will be in part obvious from the accompanying drawings, and in part pointed out as the description of the invention progresses.

In describing the invention in detail, reference will be made to the accompanying drawings, in which like reference characters designate corresponding parts throughout the several views, and in which:

Fig. l is a side view of a relay having contacts constructed and related to its armature in accordance with the present invention, with certain parts shown in cross-section as taken on line il of Fig. 4;

Fig. 1A is a sectional view taken on line lA-|A of Fig. 1 to show the contact structure in greater detail;

Fig. 2 is a sectional view taken on line 2-2 of the same relay shown in Fig. 4, but at a point between its two pole pieces so as to bring out in detail the backstop for the armature together with a spring biasing means for the armature as proposed in accordance with the present inven-- tion;

Fig. 3 shows a side view of a different type relay constructed to have non-bounce contacts as provided in accordance with the present invention; and

' Fig. 4 is a front sectional view to show the relative position of the contacts and the backstop; and this view is taken on line t-A of Fig. 2.

Referring to Fig. 1, a relay of the same general type as disclosed in the prior Pat. No. 1,749,331, dated March l, 1930, to O. S. Field, and more particularly used in railway signalling systems, is shown in cross-section as having a base plate 5 of molded insulating material, extending pole pieces a cooperating armature 1 and energizing windings 8 located on the pole pieces above the base plate. At the back of the relay, a bracket support fl, running lengthwise of the relay, is held in a suitably adjusted position by the adjustable studs two at each end, which are attached to the base plate 5.

The bracket support 9 has a downwardly bent trunnion support at each end, which trunnion support has a hole for receiving its respective trunnion. A bifurcated bearing arm l l is located at each end of the armature l preferably by being riveted thereto. Each of these two bearing arms has a suitable trunnion l2 inserted in its bifurcated portion which is then tightened by set screw 13 to hold the trunnion in a proper position. In other words, the armature i is pivoted on two trunnion 12, one at each end of the armature. The armature is also supplied with one or more residual pins I4, located along its surface cooperating with the pole pieces t, and preferably along the forward edge of the armature. These residual pins Hi are, of course, of the proper thickness to determine the minimum air-gap between the armature 1 and the two pole pieces 6.

Referring to Fig. 2, it will be seen that a backstop member 15 is supported by the base plate 5 by a bolt i6. This backstop. member H) has an extending arm l1 through which a set screw I8 passes to the proper position to act as a backstop for the armature and in which position it is held by the lock nut 19. This backstop member is located substantially at the center of the relay as can be understood from Fig. 4 where the arm [1 is shown in section.

A recess in the base plate 5, and located between the two extending pole pieces 6, receives a bias spring at which is of the compression type. The lower end of this bias spring fits over the conical-shaped adjusting screw 2| which passes through a threaded hole in the armature and is I held in position by loch nut 22. A washer 23 with a conical-shaped center hole is located between the conical-shaped end of the set screw 21 and the spring 26. By having the conical-shaped washer 23 ride on the end of the screw 21, the spring 28 can be further compressed as the screw 2| is caused to extend further above the armature surface. In other words, the washer 23 rides on the end of screw 2! so that the spring 20 may be compressed or released as the set screw 2| is adjusted without turning the spring. In this way, the desired tension may be obtained to give the necessary biasing effect.

Returning to Fig. 1, it will be noted that a bracket is connected to the base 5 by a suitable terminal bolt 255. This bracket 25 has a right angle extension at its lower end upon which is mounted what may be termed a contact block. This contact block is an assembly of insulating pieces, contact fingers, limit arm, connector, and face plate, all attached to the bracket 25 by suitable bolts 35. More specifically, the movable contact finger 21 is adjacent the bracket 25 to make electrical contact therewith, but is separated from the contact limit arm 29 and stationary contact finger 28 by insulating piece 30. The limit arm 29, stationary contact finger 28 and terminal con hector 32 are adjacent each other so as to make electrical connection with each other. The terminal piece 32 is connected through wire 33 with the terminal post 34. The stationary contact finger 28 is separated from a metal face plate 42 by insulating piece 3!. The contact finger 28, limit arm 29, connector 32 and insulating pieces 30' and 3| have sufliciently large holes through them as to receive bolts 35 with insulating tubes 43 located over them so as to assure complete electrical isolation of the contact finger 28 from the contact finger 21.

It is noted that the stationary contact finger 28 has a contact button 36 of suitable contact material, such as silver, riveted thereto. The movable contact finger 21 has its free end stiffened by having a fiat metal piece 31 soldered thereto to give added rigidity. Suitable holes are made in the pieces 21 and 31 so as to receive riveting extensions of arcuate contact 38 adapted to cooperate with the contact button 36 (see Fig. 1A). The arcuate contact 38 is, of course, soldered to finger 21 to give more perfect electrical connection. The contact fingers 21 and 28 are preferably made of Phosphor bronze but may be of any other suitable resilient material.

The movable contact finger 21 is made of relatively thin flexible material and has such a length in comparison to its reenforced free end and the Weight of the arcuate contact 38 as to have its center of gravity located approximately at the center of the arcuate contact 38. The stationary contact finger 28 is made of a relatively thicker flexible material so that although it is a shorter finger, its weight is very nearly the same as the weight of the longer movable contact finger 21. Due to the relative lengths, masses, and degrees of resiliency, the two contact fingers 21 and 28 have different natural frequencies of vibration. In one form of device constructed to embody the present invention, it was found that the desired characteristic features would be obtained by having frequencies of vibration for the two fingers 21 and 28 of a relationship of approximately two to one, i. e. the natural frequency of the stationary contact finger 28 was approximately twice the natural frequency of the movable contact finger 21.

The limit or stop arm 29 is of a relatively heavy nonresilient material to sunny a positive stop for the contact finger 28. This limit arm 29 has a shape so as to contact the finger 28 at a suitable point along its length such as at the point 39. The stationary contact finger 28 is so adjusted that a particular trapped pressure is created for the contact finger 28 which causes it to be held against the stop arm 29 at point 33. The movable contact finger 21 is so adjusted that it produces a normal contact pressure against the stationary contact finger 28 which is slightly less than the amount of trapped pressure applied to the contact finger 23. In one form of device constructed to embody the present invention, it was found that the characteristic features of the present invention were obtained by making the normal contact pressure of finger 21 in the amount of approximately three-fourths of the particular trapped pressure applied to the contact finger 28. In considering the contact pressures, it is to be understood that they are measured from points closely adjacent where the arcuate contact 38 engages the contact button 36. In other words, the trapped pressure of contact 23 is not the actual pressure applied to the stop arm 29 but rather the force exerted at the contacting point of button 36.

Connected to the armature I are two insulating studs 40 which support a contact operator 4 i. In other words, the contact operator 4! is mechanically fastened to the armature through insulating means so as to be electrically isolated from other contacts connected to the same armature. This contact operator 4! extends outwardly to engage the free end of movable contact finger 21, so that when the armature I is attracted toward the pole pieces 6, the contact operator 4| will have a short distance of free travel before it engages the finger 21 and positively lifts it away from the finger 28. It is noted that the contact operator 4! has a slightly raised portion at its center (see Figs. 1 and 4) so that as it engages the end of the contact finger 21, it lifts it in a balanced fashion without causing one side of the arcuate contact 33 to remain on the contact button 36 longer than the other.

The structural characteristics of the contact and relay arrangement contemplated in accords ance with the present invention has been described in particular with respect to Figs. 1 and 2, and this structure has been found in practice to operate in such a positive fashion that no contact bounce or distorted contact operation is ascertainable even by the use of an oscilloscope. However, the exact reasons and mode of operation of such a contact and operating mechanism may be theoretically described in various ways, the following consideration of its operation being given merely for the sake of definiteness in the disclosure and without any desire to limit the scope of the invention.

It is a known principle of physics that when a mass A strikes an equal mass B, the momentum of mass A is transferred to the mass B so that the mass A stops its motion and the mass B proceeds with nearly the same velocity. This, of course, assumes that the two masses are made of very highly elastic material. If the mass A is slightly greater than the mass B, it transfers a major portion of its momentum to mass B and retains a portion that tends to cause it to continue to move in the same direction.

As above mentioned, the contact finger 21 is contemplated in accordance with the present in,- vention as having substantially the same mass as the contact finger 28. Thus, when the armature T releases, the contact operator 4| moves downwardly and allows the arcuate contact 38 to strike the contact button 36 with a force including a momentum component and an accelerating component due to the initial bias of the contact finger 21. This combined force tends to move the contact finger 28 downward, but since the mass of the contact finger 21 is the same as (or substantially the same) the mass of the contact 28, and is also accompanied by the accelerating force of its normal spring tension, it tends to follow the contact 26 in any such slight downward motion. However, the normal spring tension of the contact finger 21 is less than the normal trapped spring tension of contact finger 28 so that it cannot force the contact finger 28 away from its stop arm 29 at the point 39. Any slight movement of the contact button 36 at the end of the contact finger 28 is more the result of a wave of vibration in the finger 28. This might cause the finger 28 to vibrate at its natural frequency, but such vibration is substantially critically clamped by the frictional engagement of the stop arm 29 at point 39 against the contact finger 28, so that any slight downward movement of the contact button 36 results in its immediate restoration to its normal position. Since the natural frequencies of the contact fingers 21 and 28 are substantially diiferent, any tendency of one to vibrate upon impact with the other is damped by reason of such contact.

It is noted that the particular trapped pressure between the contact finger 28 and the stop arm 29 is of a particular value, which, of course, must be determined in accordance with the natural frequency of the contact finger 28. By this, it is not meant that the value is exact but that it must be Within a given range of pressures in order to provide the desired damping operation.

As above mentioned, the contact between the two fingers 2i and 23 tends to damp any vibrations set up in the contact fingers by reason of the impact, and this is, of course, in addition to the damping characteristics of the stop arm 29 for the contact finger 28.

In addition to the above, it is desirable to minimize any vibration that might be set up in the contact finger 21, which, of course, does not have any other damping means associated with it. For this reason, the reinforcement of the free end of the finger 2'! is made of such a weight as to bring the center of percussion substantially to the arcuate contact 38. It is, of course, preferably that the center of percussion fall at the center of the arcuate contact 38, because when this is true the impact does not set up any vibrations in the finger 21. By proper choice of the size and weight of the materials involved the center of gravity and the center of percussion can be made to coincide at the arcuate contact 38.

When the armature I is fully released, the contact operator 4| is mechanically independent of the free end of the contact finger 21. Thus, the impact of the armature 1 against the backstop screw I8 and any consequent vibrations are not communicated to the movable contact finger 21. This impact of the armature I with its back stop screw 1 8 is preferably minimized by providing the magnetic structure with short circuited windings or the conventional copper washers around the pole pieces. These short circuited turns tend to make the relay armature 1 slow in releasing and increases its transit time from its operated position to its released position thus reducing the momentum in the armature structure. In this way, any vibrations that might be communicated via the base structure of the relay to the contact block and fingers 21 and 28 is minimized.

As above mentioned, the spring 20 tends to hold the armature 1 against the backstop [8 so that any external vibrations that might be communicated to the armature will be reduced to such a point that the contact operator 4! does not touch the free end of the movable contact finhesitation in its movement may cause the same effect as a contact bounce when the armature is released; and for this reason, the armature must be operated in a positive smooth fashion.

It is noted that when the armature 1 reaches its fully operated position, impact is made with the pole pieces at the residual pins 14. However, any vibrations that may be caused by such impact and transmitted to the movable contact finger 21 either via the contact operator 4! or the base structure of the relay is ineffective to act on any of the circuits governed by the contacts of the relay, because at such time the contact fingers 21 are in their operated or raised positions. In other words, slight vibration of the movable contact finger 21 when not in physical contact with the stationary contact 28, can do no harm.

Another form of the invention is shown in Fig. 3, wherein a relay of the general type shown in the prior Pat. No. 2,258,122 granted October 7, 1941, is disclosed as having a contact organiza tion constructed as proposed in accordance with the present invention. This relay of Fig. 3 comprises in general two cores which are con nected by a backstop 5| adjacent the molded insulated base 52. Two windings 53 are located on the cores for energizing them to actuate an armature 54 which is normally biased to a dashergized position (as shown) by a spring 55. The armatures deenergized position is determined by the setting of the screw 56 while its energized position is determined by the setting of screw 51.

On the base plate 52 is mounted a contact block 58 which has contact springs 59 and 80 constructed as described in connection with Figs. 1 and 1A. A stop arm BI is provided for the contact finger 59 so as to provide the initial trapped pressure as previously described. The movable contact finger 60 is operated by a pusher 62 which is mounted on two springs 63 and 64 in a manner to operate substantially parallel to the base plate 58 as the armature 54 is actuated causing the arm 65 to lift the pusher 62. As the arm is actuated it is apparent that there is a certain amount of free movement before the pusher reaches the movable contact 60 after which it is lifted away from the finger 59. With this organization, it is apparent that a plurality of groups of contacts may be readily operated and that the armature is wholly mechanically free from the movable contacts while it is deenergized.

It is to be understood that the construction of the contacts in this Fig. 3 is exactly the same as disclosed in Figs. 1 and 1A and as previously described. The contacts 59 and 6%] are to have the same relative frequency characteristics; and the contact finger is reinforced at its end in exactly the same way as the contact 21 in Fig. 1. The arcuate contact 66 is preferably located so as to be at the center of percussion. This structure provides the same nonbounce characteristics as described in connection with the form shown in Fig. 1. The shape of the stop arm 61 is slightly different in this form merely to indicate that such shape is immaterial to the proper operation of the means embodying the present invention.

Referring to Fig. 1, it will be seen that only a single contact group has been shown, but in Fig. i there is indicated that there is a plurality of contact operators 4! attached to the armature; and it is assumed that there is a contact group associated with each such operator. The same situation is true with respect to the modification of Fig. 3 in that it should be understood that a plurality of vertical rows of contacts may be located side by side and operated by the armature the same as shown.

Both in Fig. 1 and Fig. 3 it also should be understood that the various contacts are connected to circuits which they control in any desired fashion.

Having shown and described two forms of an electromagnetic relay and the novel contact structures associated therewith as specific embodiments of the present invention, it is desired to be understood that these forms are selected to facilitate in the disclosure of the invention rather than to limit the number of forms which it may assume; and, it is to be further understood that various modifications, adaptations and alterations may be applied to the specific form shown to meet the requirements of practice, without in any manner departing from the spirit or scope of the present invention.

What I claim is:

1. In a tractive type relay having a pivoted armature, a rigid contact operator fixed at one end to the armature, a fixed contact block, two spaced flexible contact fingers each connected at one end to said contact block and said one of said contact fingers being longer than the other, a rigid stop arm located between said two contact fingers and attached at one end to said contact block with its other end bearing against the shorter of said contact fingers to: produce a predetermined trapped pressure, said longer contact finger being biased to normally bear against said shorter contact finger with a force less than said predetermined trapped pressure, and the free end of said longer contact finger extending outwardly from said contact block to a point to be engaged by said rigid contact operator when said armature is operated but allowing an initial free movement of said armature before engaged by the contact operator, whereby said armature is wholly disconnected from said longer contact when in a released position.

2. In a tractive type relay having a pivoted armature, a fixed contact block, a plurality of pairs of contact springs connected to said block, the springs of each pair being biased towards each other and one spring of each pair being longer than the other, a rigid contact operator operatively connected to the pivoted armature of the relay and having a plurality of spaced slots for receiving the extending ends of the longer of said contact springs, said slots being sufficiently large that said contact operator is wholly free from said contact springs when the armature is in its initial position but is operative to engage said contact springs and move them away from the other spring of each respective pair when the armature is actuated.

3. In a tractive type relay having a pivoted armature, a rigid contact operator attached to the armature, a fixed contact block, two spaced fiexible contact springs, one slightly longer than the other, and both attached to said contact block, said contact springs being of different thickness to give distinctly different natural periods of vibration, contact points connected to the free ends of said springs so as to cooperate when said springs approach each other due to their initial trapped pressure, said contact block being so located that the actuation of said armature causes said contact operator to engage the longer of said two contact springs and move it in a direction away from the other contact spring, said contact operator being slightly spaced from said extending portion of said longer contact finger when said armature is in its initial position.

4. In a relay structure, two contact springs anchored at one end and electrically isolated from each other, said contact springs being biased toward each other to cause their free ends to make electrical contact with each other, said free end of one of said contact springs extending outwardly beyond the other contact spring, a rigid stop arm located between said two contact springs and anchored at one end with its other end touching the short contact spring to give -it a predetermined trapped pressure, a movable armature having an extending operating arm assuming a position adjacent said extending end of the long contact spring but with a free space between them, said operating arm being effective upon the actuation of said armature to touch the long contact spring after the initial free travel of the armature and then move the long contact spring away from the short contact spring, said contact springs having substantially the same mass, and said rigid stop arm giving a near critical damping efiect on said short contact spring when said. armature moves to a position where its extending arm no longer touches said long contact spring.

5. In a relay structure having a pivoted armature, a fixed contact block of insulating material, two spaced contact springs attached to said block, one of said springs being longer than the other and having a lower natural frequency of vibration, contact points located on said contact springs at equal distances from said contact block near their free ends, the contact point on the longer one of said springs being located at substantially the center of percussion of that spring, and means connected to the armature of the relay for operating the longer one of said two contact springs away from the shorter one.

6. In a relay structure having a pivoted armature, a contact block of insulating material mounted on the relay, two spaced contact springs attached to said block and provided with an initial bias towards each other, one of said springs being longer than the other and having a lower natural frequency of vibration, contact points attached to each of said springs at equal distances from said contact block near their free ends and attached to cooperate with each other, the contact point on the longer one of said contact springs being located at substantially the center of percussion of that spring, a rigid stop arm located between said two contact springs and attached at one end to said contact block with its other end bearing against the shorter one of said contact springs to produce a predetermined trapped pressure, said longer one of said contact springs being biased toward the other contact spring to normally bear against it with a trapped pressure substantially less than said predetermined trapped pressure, and means connected to the armature of the relay for operating the longer one of said two contact springs.

7. In a relay structure having a pivot armature, a fixed contact block of insulating material mounted on the relay, two spaced contact springs attached to said block in such a way that they are movable in the same plane, one of said contact springs being longer than the other and having a lower natural frequency of vibration, a contact point on each of said springs at equal distances from said contact block to cooperate with each other, the contact point on the longer one of said springs being located near the center of percussion of that spring, a rigid stop arm located between said two contact springs and attached at one end to said contact block with its other end bearing against the shorter of said contact fingers to produce a predetermined trapped pressure and effect substantially critical damping when that contact finger is initiated into a vibratory motion, said longer one of said contact springs being biased to normally bear against said shorter contact finger with a trapped pressure of approximately threefourths of said predetermined trapped pressure, and the free end of said longer one of said contact springs extending outwardly beyond the free end of the shorter one of said contact fingers, and means connected to the armature for operatively engaging the extending portion, of the longer one of said two contact springs.

8. In a tractive type relay having a pivoted armature, a rigid contact operator attached to the armature, a fixed contact block attached to the relay, two spaced flexible contact springs attached to said contact block, one of said con-tact springs being longer than the other, a rigid stop arm located between said two contact springs and attached at one end to said contact block with its other end bearing against the shorter of said contact springs to produce a predetermined trapped pressure, said longer one of said contact springs being biased to normally bear against said shorter contact spring with a force less than said predetermined trapped pressure, and the free end of said longer one of said contact springs extending outwardly from said contact block to a point to be engaged by said rigid contact operator when 'said armature is operated but allowing an initial free movement of said armature before being engaged by the contact operator, said pivoted armature being biased by gravity to a non-operated position, and a spring means for additionally 'biasing said armature to a non-operated position, whereby said armature is wholly disconnected from said longer one of said contact springs when it is in a non-operated position and the additional spring biasing means acts to maintain any movement due to external vibrations to be of a magnitude less than required to cause said'rigid contact operator to engage its associated contact spring.

9. In a tractive type relay having a pivoted armature, a plurality of rigid contact operators attached to said armature, a plurality of fixed contact blocks, each block having a pair of spaced flexible contact fingers connected thereto and one finger of each pair being longer than the other to to be adapted to be engaged by its respective contact operator but normally being physically disconnected therefrom, and means associated with each pair of contacts for determining the initial position of each of the shorter of said pair of contacts.

10. In a tractive type relay having a pivoted armature biased to a particular position, a fixed contact block having two spaced contact springs attached thereto, one of said springs being longer than the other and also having a lower natural frequency of vibration than the other, contact points located near the free ends of said contact springs, and means connected to the armature for operating the longer of said two contact springs, said means being physically disconnected from said longer contact spring when said armature is in one of its positions.

11. In a tractive type relay having a pivoted armature operable to either of two positions, a fixed contact block having two spaced contact springs attached thereto, said contact springs being biased toward each other and one of said springs having a lower natural frequency of vibration than the other, contact points located near the free ends of said contact springs, a back stop member for limiting the extent of movement of one of said springs when the other is moved away from it, and means operated by said armature for moving said other spring away from said one spring when said armature moves to one of its positions, said means being wholly disconnected from said other spring when said armature moves to the other of its positions, whereby said other contact spring is physically independent of said "armature when the armature is in the other of its :positions thereby preventing any vibration of said armature from being transmitted to said other contact spring.

12. In a tractive type relay having a pivoted armature operable to either of two positions, a fixed contact block having a plurality of pairs of contact fingers attached thereto, one contact of each pair being relatively fixed and the other contact of each pair being biased toward it, a contact finger operator operatively connected to said armature and constructed to move said other References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,162,571 Chubb Nov. 30, 1915 1,531,347 Rhodes Mar. 31, 1925 2,265,297 Little Dec. 9, 1941 2,362,855 Stimson Nov. 15, 1944 2,518,030 Kuperus Aug. 8, 1950 FOREIGN PATENTS Number Country Date 341,348 Germany Sept. 29, 1921 

